Sweetening of sour hydrocarbons with transition metal compounds



July 21, 1964 T. J. WALLACE ETAL 3,141,342

SWEETENING OF SOUR HYDROCARBONS WITH TRANSITION METAL COMPOUNDS Filed Feb. 21. 1961 COMPARISON OF COBALT PYROPOSPATE & DISECONDARY BUTYL PHENYLENE DIAMINE COBALT PYROPOSPHATE DISECONDARY BUTYL PHENYLENE DIAMINE RSH (mg/|O0c.c.) w m m 5 3 5 TIME HOURS Thomas J; Wallace Alon Schriesheam Inventors Hons B. Jonossen By MUM M 4 A Patent Attorney United States Patent O 3,141,842 SWEETENING F SOUR HYDROCARBONS WITH TRANSITION METAL COMPOUNDS Thomas J. Wallace, Elizabeth, and Alan Schriesheim,

Berkeley Heights, N..l., and Hans B. Jonassen, New

Orleans, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed Feb. 21, 1961, Ser. No. 90,754 15 Claims. (Cl. 20S206) This invention relates to a process of sweetening sour petroleum distillates comprising contacting said distillates with an inorganic transition metal complex compound. More particularly, this process relates to sweetening petroleum distillates containing sulfur compounds. Specifically, this invention relates to a process of sweetening sour petroleum distillates containing mercaptans and mercaptide compounds comprising contacting the distillates with an inorganic transition metal complex oxidation catalyst which converts the mercaptans and mercaptides to disulfides.

In the manufacture of light hydrocarbon oils and motor fuels by modern cracking methods, substantial amounts of mercaptans are formed when sulfur-containing heavy oils are used for cracking stocks. In fractionating the cracked products, the mercaptans become concentrated in the light fractions normally used for gasoline and fuel oils. The mercaptans impart a highly objectionable odor to the fraction, decrease the octane number, and must be removed or converted to less objectionable substances before it is suitable for blending into a marketable product.

There are several processes being used for thepurpose of removing the mercaptans before converting them to the less objectionable disulfides. These processes have to a greater or lesser degree the disadvantage of requiring extensive equipment for handling the large volumes of treating agent required. In some of these processes, relatively expensive treating agents are used. Large losses of some of the reagents occur and frequently the oxidizing agents end up in the product, which may be undesirable. The oxidation catalysts of the present invention are sufiiciently active to sweeten sour distillates having a comparatively high mercaptan content; however, it is preferred to remove a major portion of the mercaptans from the distillate prior to final sweetening. For

gasoline to which alkyl lead compounds are not to be added, the presence of the disulfides is not particularly objectionable. On the other hand, the presence of disulfides in gasoline to which alkyl lead compounds are to be added is objectionable because the presence of the disulfides reduces the sensitivity of the gasoline to the addition of the lead to even a greater extent than a corresponding concentration of mercaptans. Since most gasolines now marketed aretreated with tetraethyl lead or tetramethyl lead, it follows that it is desirable to remove most of the mercaptans rather than to merely convert them to disulfides. Conventional treating methods can remove from about 50 to 95% of the mercaptans, but still leave sulficient mercaptans to produce a product which is sour. Applicants have found efiicient complex inorganic metal oxidation catalyst compounds which effectively and efficiently reduce the mercaptans present in the petroleum distillate to a value which gives a negative doctor test and is accordingly doctor sweet.

The hydrocarbon mixture containing mercaptan com- 3,141,842 Patented July 21, 1964 pounds is said to be sour or positive to the doctor test if it contains more than about 004% sulfur, calculated as mercaptans. This relates to a mercaptan number (RSI-I No.) of 0.4. It is said to be sweet or to be negative to the doctor test when the sulfur concentration is below that value. The mercaptan number is defined as the milligrams of mercaptan sulfur per 100 milliliters of oil, and is generally determined by titration with standard copper salt solution. The doctor test is more fully described in US. Patent 2,543,953, dated March 6, 1951.

It is an object of the present invention to provide an etlicient and economic method for sweetening sour petroleum distillate mixtures. It is another object of the present invention to provide a method for removing a portion of the mercaptan content of a sour hydrocarbon mixture and then sweeten the partially demercaptanized, but sour, hydrocarbon mixture to give a negative doctor test. A further object of this invention is to carry out the sweetening by contacting the sour distillates with an aqueous mixture containing the oxidation catalyst or with fixed bed oxidation catalysts. A still further object of this invention is to produce a doctor sweet hydrocarbon mixture without pretreating said mixture to remove mercaptains. The catalysts of this invention possess several distinct advantages over the prior art catalyst. They are commercially available and/or easily prepared. They are water soluble, do not contaminate the product, and are about one-tenth as expensive as some of the conventional catalysts used to sweeten petroleum hydrocarbons.

In one embodiment of applicants invention, a sour petroleum distillate is sweetened by contacting the distillate with an inorganic transition metal complex oxidation catalyst to produce a composition which is negative to the doctor test. Another embodiment of applicants invention is to first reduce the mercaptan sulfur content :of a petroleum distillate by treatment with the conventional aqueous caustic wash, and then to contact the partially sweetened distillate with the oxidation catalyst of this invention.

In a preferred embodiment of the invention, a sour petroleum distillate containing mercaptan compounds is first treated in a conventional manner with an aqueous caustic solution to remove from 50 to of the mercaptans present, leaving sutficient mercaptans in the petroleum distillate to give a mercaptan number of between 3 and about 40 or more which gives a positive doctor test. This sour distillate is contacted with a sufficient amount of a mixture of an aqueous caustic solution containing the complex inorganic metal catalyst of this invention for a suflicient period to reduce the mercaptans to a value which gives a negative doctor test, resulting in a sweetened distillate. The catalyst is first thoroughly mixed with the aqueous caustic solution, in which it is soluble, and then contacted with the distillate. either concurrently as in the continuous process, or in a stirred reactor as in a batch process. Sweetening of the sour hydrocarbon distillate is affected by oxidation of the 'mecaptans to disulfides. Accordingly, an oxidizing agent is present in the reaction mixture. Air is preferred, although oxygen or other oxygen-containing gases may be utilized. Depending upon the content of mercaptans in the distillate, there may already be sufiicient entrained or dissolved oxygen or air in the distillate to accomplish the desired sweetening. However, when the distillates containing high concentrations of mercaptan are sweetened, it is generally necessary to introduce some air into the reaction. This may be done by bubbling air into the reactor or contacting vessel. In a continuous process, the caustic containing the catalyst is passed countercurrently to an ascending stream of sour petroleum distillate. In a batch type process, the reaction zone contains the alkaline solution and catalyst, and the gasoline and air are mixed in the reaction zone; the mixture is allowed to settle and sweetened gasoline is removed from the upper portion of the reaction zone. The sweetened petroleum distillate can be washed with water to remove any entrained caustic. The reaction temperature is not critical, but should not be so high that vaporization, cracking or undesirable side reactions take place. Usually, the reaction is carried out at ambient temperatures. Pressure is not critical and usually the reaction is carried out at atmospheric pressure. However, where high temperatures are used high pressures can be utilized in order to keep the reactants in the liquid phase. The reactants are contacted with the catalyst for sufiicient time so that the distillate being treated is substantially reduced in mercaptans present and a sweet distillate results. This can take from a few minutes up to ten days or more.

Due to the high activity of our complex inorganic metal catalyst compounds, very small amounts of the catalyst can be used. The catalysts are not soluble in the hydrocarbon layer, and the oxidation takes place at the aqueous caustic-hydrocarbon interface. Since the catalyst is present in the aqueous layer and does not dissolve in the hydrocarbon layer and does not itself take part in the reaction, the sweetened hydrocarbon product does not contain any of the catalyst.

Petroleum distillates containing mercaptan and mercaptide compounds can be sweetened in accordance with this process. Various petroleum distillates, such as virgin and cracked naphthas, kerosene, gas oil, heating oil, fuel oil, gasoline and the like, may be sweetened in accordance with our process. Crude and residual oils may also be sweetened. Oxidation of the mercaptans to disulfides is carried out by contacting them with our novel catalyst in the presence of base and oxygen or air.

The inorganic transition metal complex oxidation catalyst compounds used in applicants invention are, for example, phosphorous compounds of vanadium, cobalt, nickel, and iron. Examples of these compounds are cobalt pyrophosphate, vanadium pyrophosphate, nickel pyrophosphate, and iron pyrophosphate. Other derivative compounds of the above mentioned transition metals may also be used, such as the molybdates, tungstates, thionates, and thiosulfates. Examples of these compounds are cobalt molybdate, cobalt tungstate, cobalt thionate, vanadium molybdate, vanadium tungstate, vanadium thionate, nickel tungstate, iron thionate, cobalt thiosulfate, cobalt tetrathionate, and cobalt pyroborate. Additional specific compounds that can be used are phosphonitriles of the following formula:

wherein M is selected from the group comprising cobalt. vanadium, nickel, and iron and X is selected from the group comprising OH and NH The preferred inorganic complexes are the pyrophosphates and molybdates of cobalt, vanadium and nickel. All the above compounds function as oxidation catalysts and do not themselves take part in the reaction. They are capable of being used for an extensive period of time and, since they have appreciable activity, may be used in very small concentrations.

A fixed bed catalyst can be prepared by impregnating or coating an inert porous granular material, such as fullers earth, bauxite, humus, charcoal, or molecular sieve zeolites, alumina, aluminum silicate and the like, with the complex inorganic metal catalyst. The catalyst bed is first saturated with a soluble phosphorous or molybdate compound and then soaked or sprayed with a soluble dilute transition metal salt of cobalt, for example, whereby the inorganic cobalt complex compound is formed in situ within the pores and on the surface of the carrier material. The catalyst is then washed and dried prior to use. For example, in making cobalt pyrophosphate, the catalyst bed is first soaked with pyrophosphoric acid at a temperature of ISO-200 C. At this temperature, the bed is contacted with cobalt chloride. The cobalt pyrophosphate precipitate and is formed on the surface and in the pores of the carrier. HCl gas is evolved, leaving a solid product. The catalyst bed and product are washed with ethanol or water to remove unreacted ingredients and dried. Instead of precipitating the cobalt pyrophosphate on the fixed bed, it can precipitate in situ and separate as a solid. The solid is ground into a fine powder and may be used to either impregnate or coat a fixed bed carrier material or may be redissolved in an aqeuous caustic solution to be used as a liquid catalyst. In a similar manner cobalt molybdate can be precipitated on a fixed bed of charcoal, aluminum silicate or alumina.

An aqueous catalyst solution containing cobalt pyrophosphate can be prepared by dissolving 0.2 mole of sodium pyrophosphate and 0.1 mole of cobalt nitrate in 800-900 cc. of water. The mixture is then diluted to 1 liter and can be used as an aqueous catalyst composition to sweeten sour petroleum distillate. This composition contains 0.10 mole of cobalt pyrophosphate catalyst.

The tungstates, molybdates, thionates, thiosulfates and pyrophosphates of cobalt, vanadium, nickel, and iron may be made in a similar manner. The temperature at which the sweetening process is carried out is not critical. The reaction may be carried out at temperatures up to those at which the petroleum distillate begins cracking and undesirable byproducts and side reaction take place. Preferably, the reaction is carried out at about ambient tempera tures. The pressure at which the reaction is carried out is not critical; however, where higher temperatures are used, sufficient pressure is required to maintain the reactants in the liquid phase and to prevent vaporization of the distillate. The reactants are maintained in contact with the catalyst for a few minutes or less up to ten days or more, preferably for a period of a few minutes up to 24 hours, and specifically, for a few minutes up to about 10 hours. Where a fixed bed catalyst is used, a 0.1 to 10 volume of hydrocarbon to the volume of catalyst per hour can be used. Generally, 0.1 to 5 v./v./h. is used, and specifically, 0.5 to 1 v./v./h. is preferred. The concentration of caustic used will depend upon the amount of mercaptans present which will depend on whether or not the sour petroleum distillate has previously been treated to remove from 50 to about 9 5% of the mercaptans originally in the distillate. Where the distillate was not previously treated to remove the major amount of mercaptans, and the distillate has a mercaptan number up to about 40, the concentration of caustic used can be 10-50% with up to 5% caustic solution by volume of distillate treated. Where the distillate was previously treated to remove the major amount of mercaptans present, the concentration of caustic can be 10-30%, and is preferably about 20-30%. Frequently the amount of caustic entrained in a feed from the previous caustic pretreatment is sufficient. The catalyst is very active, is used in minor amounts, and is not contaminated or used up by the reactants. The concentration of catalyst that is used can be .1 to parts per thousand, based on the volume of oil treated. Though concentrations of 3 to 10 parts per thousand are preferred, concentrations of 1 to 1 00 parts per thousand can also be used. However, it is noted that greater amounts of catalyst may b used without adverse effect, and the amount used'is generally is utilized. The aqueous caustic solution containing the catalyst is introduced at the top of the vessel and passes downward countercurrently into an ascending stream of sour hydrocarbon. The sweetened hydrocarbonis removed from the top of the vessel and the catalyst is removed from the bottom of the vessel and recycled to the top and re-used again. A fixed bed catalyst can also be used in this type of apparatus in which case it would be set inside the apparatus in such a manner that it is brought into intimate contact with the descending hydrocarbon stream. However, where a fixed bed catalyst is used, it is desirable that the hydrocarbon feed be first mixed with an aqueous caustic solution. This is desirable because the oxidation takes place at the aqueous hydrocarbon interface and because it is the alkali salts of the mercaptans that are oxidized. Where a liquid aqueous caustic catalyst composition is used in a batch process any of the various types of reactors can be used. In each case, whether a continuous or batch process is used, where additional air is needed to carry out the oxidation of substantially all of the mercaptans present, it can be introduced into the distillate feed stream or bubbled directly into the reactor.

In a preferred embodiment of the invention, sour petroleum distillate which has been previously treated with a conventional caustic wash to remove 50 to about 95% of mercaptans, leaving a product still containing sufficient mercaptans to produce positive doctor test, i.e., is sour, is introduced countercurrently to a descending stream of aqueous caustic complex inorganic catalyst composition in the presence of a rising stream of air. The sour petroleum distillate vcontaining sufiicient mercaptan to have a mercaptan number of 3 to is contacted at a rate of 0.2 to 1.0 v./v./h. with up to 5% by volume of an aqueous caustic solution containing -30 weight percent of an alkaline hydroxide, such as sodium or potassium hydroxide, and containing a concentration of 5-10 parts per thousand of a pyrophosphate of the transition metals, based on feed, for about 1-6 hours. Air is continuously bubbled through the reactor and sweetened petroleum distillate is Withdrawn from the'top and taken to storage. Aqueous caustic catalyst solution is withdrawn from the bottom and recycled to be used in the reaction again. After about 6 hours, it is found that the mercaptan number of the sweetened petroleum distillate has been reduced to about 0.30. This gives a negative doctor test. Prior to sending the sweetened gasoline to storage, it may be subjected to a water wash to remove any entrained caustic solution. In such case, the petroleum distillate can be passed countercurrently to a descending stream of wash Water. The aqueous caustic layer is removed from the lower portion of the vessel, while the sweetened gasoline is removed from the top and taken to storage. This sweetened gasoline is free of pyrophosphate catalyst. In order to show the efficiency of applicants novel complex inorganic transition metal oxidation catalyst, the data presented below in Table I, shows the comparative effectiveness between our catalyst and the conventional disecondary butyl phenylene diamine catalyst.

Table I In each case 300 cc. of light cat. naphtha having an initial mercaptan number of 15 (RSH #15) was treated with the respective catalyst in the presence of air and base. The. sweetening was carried out for a period of six hours-anda checkof the'mercaptan number was made every hour with the following results:

Cobalt Pyrophosphate 1 Diseeondary butyl phenylene diamine 2 Tune (hr) RSH Time (hr.) RSH 1 Catalyst composition comprised 40 cc. of 0.1 mole of cobalt pyrophosphate made in accordance with reaction described in columns 3 and 4 of the specification;

2 Catalyst composition comprised 80 mg. of disecondary butyl phenyl- 1?e w d1. FO

This .data hasbeen presented graphically in the accompanying drawing. v

It isobvious fromthe above data that the cobalt pyrophosphate catalyst is far superior to the presently used disecondary butyl phenylene diamine catalyst.

The novel inorganic transition metal complex oxidation catalyst can be used to reduce the mercaptan number in sour petroleum distillates with or without previously treating the sour petroleum distillates with a conventional caustic wash. In such case, however, the petroleum distillate retains a large amount of disulfides, which may be objectionable for some uses of the petroleum distillates; for example, in gasolines the presence of disulfides renders the gasoline less susceptible to increasing the octane ofthe gasoline by the addition of tetraethyl or tetramethyl lead. Therefore, when the petroleum distillate is to be used to make gasoline products, the sourpertrole um distillate is subjected to a conventional caustic treatment to remove from 50 to of mercaptans present, and the remaining sour petroleum distillate is treated in accordance with this invention to give a negative doctor test.

As hereinbefore set forth, final sweetening of the gasoline may be preceded by extraction of acidic components, and particularly mercaptans, from the gasoline in any suitable manner. 7 This pretreatment preferably comprises contacting of the gasoline with an alkaline solution, usually at ambient temperature, and either in a batch or continuous process. In some cases elevated temperatures which may range up to about 200 F. may be employed. Following this treatment, the petroleum distillate will not be sweet and is subjected to final sweetening in the presence of caustic, air and the catalyst. The catalysts of this invention have other obvious utilities as oxidation catalysts in other chemical reactions where the oxidation of anobjectionable compound is desired.

The invention is further exemplified by various runs reported in the following examples. The examples show various embodiments of applicants invention.

EXAMPLE 1 A sour light cat. naphtha (B.R. 50450 F.) was treated in the conventional manner with a caustic solution to reduce the amount of mercaptans present to give a mercaptan number of about 3.0. This pretreated naphtha still produces a positive doctor test. The partially sweetened naphtha was then contacted with an aqueous caustic catalyst solution. The catalyst solution was made by dissolving 0.2 mole of sodium pyrophosphate in 800- 900 cc. of water, and adding, with stirring, 0.1 mole of cobalt nitrate. Cobalt pyrophosphate was formed in solution. This solution was diluted with water to 1 liter. The resulting solution is a 0.1 molar solution of aqueous cobalt pyrophosphate. There is sutficient caustic remaining in the light cat. naphtha from the previous conventional caustic treatment so that additional caustic does not have to be added. Three-hundred cc. of the partially sweetened naphtha were stirred in a batch type reactor with 40 cc. of the above described solution, while oxygen was bubbled through the reactor. The cobalt pyrophosphate catalyst was not soluble in a hydrocarbon layer. The reaction mixture was stirred sufliciently so that the hydrocarbon and catalyst were intimately mixed. The oxidation takes place at the hydrocarbon-aqueous caustic interface. The reaction was carried out for a period of about 6 hours and the mercaptan number was reduced from 3.0 to 0.06. The results obtained are reported in Table II below.

Table II REACTION OF COBALT PYROPHOSPHATE WITH LIGHT CATALYTIC NAPHDHA (RSH #300) B.P. mercaptan No.: Reaction time (hr.)

V Feed-300 cc. L.C.N. (B.R. 504.50 F.)+40 cc. of 0.1 molar cobalt pyrophosphate.

The sweetened naphtha was recovered by stopping the stirring and allowing the hydrocarbon and aqueous phases to separate. The aqueous catalyst phase was withdrawn from the bottom. The remaining light cat. naphtha was washed countercurrently with water to extract any remaining entrained caustic and sent to storage. The washed naphtha gave a negative doctor test.

EXAMPLE 2 A fixed bed catalyst is prepared by contacting an aqueous solution of cobaltous chloride at a temperature of 150-200 C. with a conventional aluminum silicate bed which is saturated with aqueous solution of pyrophosphoric acid. Cobalt pyrophosphate is precipitated in the pores and on the surface of the aluminum silicate carrier material. Hydrogen chloride gas is evolved during the reaction and is vented. The aluminum silicate carrier containing the cobalt pyrophosphate is washed with ethanol to remove nonreacted ingredients. Light cat. naphtha (B.R. 50-450 F.) which had been previously subjected to a conventional caustic solution treatment for removal of the major portion of the mercaptans present is contacted with the fixed bed cobalt pyrophosphate catalyst. The reaction is carried out in a stirred reactor with sufiicient stiring so that the naphtha containing traces of caustic from the preliminary caustic treatment is brought into intimate contact with the cobalt pyrophosphate catalyst. The reaction is carried out for a period of about 6 hours. The reaction mixture is allowed to settle and the sweetened naphtha is removed from the top of the reactor and washed countercurrently with water to remove any of the entrained caustic materials. Sweetening is effected at ambient temperature and pressure, and the treated naphtha withdrawn from the sweetening zone is found to be doctor sweet.

EXAMPLE 3 A cracked gasoline having a mercaptan number of 3 is subjected to sweetening by being contacted with a concentrated 20% sodium hydroxide solution, which contains 5-10 parts per thousand cobalt thiosulfate. The cobalt thiosulfate is made by contacting cobalt nitrate and sodium thiosulfate in an aqueous caustic solution. The cobalt thiosulfate forms in situ. With a throughput of about 1000 barrels per day of cracked gasoline in a continuous process, about 10 barrels of caustic solution per day are used, and air is introduced at about the rate of to cubic feet per hour into the sweetening zone. In order to efiect intimate contact in the sweetening zone, the aqueous caustic-catalytic solution containing the cobalt thiosulfate is introduced into the upper portion of the sweetening zone. The air is introduced in a conventional manner in the lower portion of the sweetening zone through a suitable bubbling arrangement. The sour gasoline is introduced at a point above the point at which the air is introduced. The oxidation reaction is conducted at ambient temperature and pressure, and the sweetened gasoline is Withdrawn from the top of the Zone and Washed in a conventional manner and taken to storage. The cracked gasoline withdrawn from the sweetening zone will be found to be doctor sweet. The rate of charging the cracked gasoline to the cobalt thiosulfate catalyst solution is about 4 v./ v./ h.

EXAMPLE 4 a A cobalt molybdate catalyst was made in accordance with the process described in Example 3. About 300 cc. of kerosene having a mercaptan number of 35 to 40 is contacted with 40 cc. of 20% sodium hydroxide containing 5-10 parts per thousand of cobalt molybdate based on feed. The reaction is carried out in a stirred batch reactor with air being bubbled through, at ambient temperature and atmospheric pressure for a period of about 8 hours. The mercaptan number is reduced from 35 to 40 to a value of about 0.35 which is doctor sweet.

EXAMPLE 5 A 0.2 molar solution of aqueous cobalt pyrophosphate prepared in accordance with Example 1 was contacted with alight cat. naphtha having a mercaptan number of about 40. Three hundred cc. of the naphtha, 40 cc. of the 0.1 molar solution of cobalt pyrophosphate, and 40 cc. of 10% sodium hydroxide solution is mixed in a stirred reactor for approximately 8 hours. The reaction mixture is allowed to settle and the sweetened light cat. naphtha is separated in a conventional manner from the aqueous catalytic phase. The naphtha is washed countercurrently with water. The washed naphtha when tested is found to have a mercaptan number of about 0.39 which is sweet.

The above examples were introduced to illustrate the novelty and utility of the present invention but not with the intention of unduly limiting the same.

What is claimed is:

1. The process of sweetening sour petroleum hydrocarbons containing sulfur compounds comprising contacting said hydrocarbons in the liquid phase and in the presence of an oxidizing agent, toconvert the sulfur compounds to disulfides, with an aqueous caustic solution containing an inorganic transition metal compound wherein the cation of said compound is selected from the group consisting of vanadium, cobalt, nickel and iron and the anion of said compound is selected from the group consisting of molybdates, tungstates, thionates, pyrophosphates and thiosulfates.

2. The process of sweetening sour petroleum hydrocarbons containing sulfur compounds which comprises contacting said hydrocarbons in the liquid phase at ambient temperature and pressure and in the presence of air with an aqueous caustic solution containing an inorganic transition metal compound wherein the cation of said compound is selected from the group consisting of vanadium, cobalt, nickel and iron and the anion of said compound is selected from the group consisting of molybdates, tungstates, thionates, pyrophosphates, and thiosulfates, the concentration of said inorganic transistion metal compound being from 0.1 to parts per 1000 based on said hydrocarbon fraction being treated, whereby the sulfur compounds are converted to disulfides and the mercaptan concentration of the hydrocarbon fraction is reduced.

3. The process of treating a sour hydrocarbon distillate which comprises contacting said distillate in the liquid phase in the presence of an oxidizing agent with an in- 9 organc transition metal phosphonitrile oxidation catalyst of the following structure:

P--X \l N N M N ll I 7 l XP P-X X-P wherein M is selected from the group comprising cobalt, nickel, vanadium and iron and X is selected from the group comprising OH and NH for a period sufficient to substantially reduce the mercaptan number.

4. The process for treating a sour gasoline fraction containing mercaptan compounds which comprises contacting said gasoline with an aqueous caustic solution, cobalt pyrophosphate oxidation catalyst and air in the liquid phase, whereby said contacting is carried out at ambient temperature and pressure for up to about 8 hours.

5. The process of treating a sour hydrocarbon distillate containing mercaptan compounds which comprises contacting said distillate in the liquid phase with cobalt pyrophosphate oxidation catalyst, aqueous alkaline reagent and an oxidizing agent for a period of time suflicient to substantially reduce the mercaptan level.

6. The process of treating a sour hydrocarbon distillate containing mercaptan compounds which comprises contacting said distillate in the liquid phase with vanadium pyrophosphate oxidation catalyst in the presence of liquid aqueous alkaline reagent and an oxidizing agent to oxidize said mercaptan compounds to disulfide compounds for a period of time sufiicient to substantially reduce the mercaptan concentration.

7. The process of treating a sour hydrocarbon distillate containing mercaptan compounds which comprises contacting said distillate in the liquid phase with nickel pyrophosphate oxidation catalyst in the presence of a liquid aqueous alkaline reagent and an oxidizing agent to oxidize said mercaptan compounds to disulfide compounds for a period of time suflicient to substantially reduce the mercaptan concentration.

8. The process of treating a sour hydrocarbon distillate containing mercaptan compounds which comprises contacting said distillate in the liquid phase with cobalt molybdate oxidation catalyst in the presence of a liqiud aqueous alkaline reagent and an oxidizing agent to oxidize said mercaptan compounds to disulfide compounds for a period of time sufiicient to substantially reduce the mercaptan concentration.

9. The process of treating a sour hydrocarbon distillate containing mercaptan compounds which comprises contacting said distillate in the liquid phase with vanadium molybdate oxidation catalyst in the presence of a liquid aqueous alkaline reagent and an oxidizing agent to oxidize said mercaptan compounds to disulfide compounds for a period of time sufiicient to substantially reduce the mercaptan concentration.

10. The process of treating a sour hydrocarbon distillate containing mercaptan compounds which comprises contacting said distillate in the liquid phase with nickel molybdate oxidate catalyst in the presence of a liquid aqueous alkaline reagent and an oxidizing agent to oxidize said mercaptan compounds to disulfide compounds for a period of time to substantially reduce the mercaptan concentration.

11.- The process of treating a sour hydrocarbon distillate which comprises contacting said distillate in the liquid phase with an inorganic transistion metal phosphonitrile oxidation catalyst of the following structure:

P-X XP \1 i! N M N N II I 7' R I II XP P X--P PX N N wherein M is cobalt and X is selected from the group comprising OH and NH for a period suflicient to substantially reduce the mercaptan number.

12. The process of treating a sour hydrocarbon distillate containing mercaptan compounds which comprises contacting said distillate in the liquid phase With cobalt thiosulfate oxidation catalyst in the presence of a liquid aqueous alkaline reagent and an oxidizing agent to oxidize said mercaptan compounds to disulfide compounds, said contacting being carried out for a period of time suflicient to reduce the mercaptan concentration of said distillate fraction.

13. The process of treating a sour hydrocarbon distillate containing mercaptan compounds which comprises contacting said distillate in the liquid phase with cobalt thionate oxidation catalyst in the presence of a liquid aqueous alkaline reagent and an oxidizing agent to oxidize said mercaptan compounds to disulfide compounds, said contacting being carried out for a period of time sufficient to substantially reduce the mercaptan concentration.

14. The process of treating a sour hydrocarbon distillate containing mercaptan compounds which comprises contacting said distillate in the liquid phase with cobalt tetrathionate oxidation catalyst in the presence of a liquid aqueous alkaline reagent and an oxidizing agent, whereby the mercaptans are oxidized to disulfides, said contacting being carried out for a period of time suflicient to substantially reduce the mercaptan concentration.

15. The process of treating sour hydrocarbon distillates containing mercaptan compounds which comprises contacting said distillates in the liquid phase with cobalt pyroborate oxidation catalyst in the presence of a liquid aqueous alkaline reagent and an oxidizing agent, whereby said mercaptans are oxidized to disulfides, said contacting being carried out for a period of time sufiicient to substantially reduce the mercaptan concentration in said distillate fraction.

References Cited in the file of this patent UNITED STATES PATENTS 1,954,488 Morrell Apr. 10, 1934 2,040,366 Egloff et a1. May 12, 1936 2,338,371 Workman Jan. 4, 1944 2,651,595 Moulthrop Sept. 8, 1953 2,740,747 Sweetser et al Apr. 3, 1956 2,769,759 Annable et al. Nov. 6, 1956 

1. THE PROCESS OF SWEETENING SOUR PETROLEUM HYDROCARBONS CONTAINING SULFUR COMPOUNDS COMPRISING CONTACTING SAID HYDROCARBONS IN THE LIQUID PHASE AND IN THE PRESENCE OF AN OXIDIZING AGENT, TO CONVERT THE SULFUR COMPOUNDS TO DISULFIDES, WITH AN AQUEOUS CAUSTIC SOLUTION CONTAINING AN INORGANIC TRANSITION METAL COMPOUND WHEREIN THE CATION OF SAID COMPOUND IS SELECTED FROM THE GROUP CONSISTING OF VANADIUM, COBALT, NICKEL AND IRON AND THE ANION OF SAID COMPOUND IS SELECTED FROM THE GROUP CONSISTING OF MOLYBDATES, TUNGSTATES, THIONATES, PYROPHOSPHATES AND THIOSULFATES. 